Current motor oil additives are either non-metal containing, or if they do contain metal, then the metals are generally calcium, magnesium, zinc, or sodium.
Recently it has been found that copper additives are particularly useful in motor oil as antioxidants. Such use has been described in Canadian Pat. No. 1,170,247 and U.K. Published Patent Application No. GB 2,056,482A both based on U.K. Application No. 7928146 by T. Colclough, F. A. Gibson and J. F. Marsh. There is generally little or no problem in formulating passenger car crankcase oils with copper additives. However, a problem has arisen in applying these copper additives to motor oils for diesel engines which are extensively used in trucks. It has become a common practice for many truck fleet operators to have samples of the engine oil periodically analyzed for metals in order to diagnose contamination, corrosion and particularly excessive wear and impending failure of engine parts. Such metal analysis will typically include: copper, which can indicate excessive wear of copper-lead bearings; iron, which can indicate excessive wear or rust of the engine; chrome, which can indicate excessive wear of chrome faced piston rings, etc. Adding a copper additive to the motor oil interferes with the copper analysis as there was no way to tell from the used oil analysis whether a high level of copper found by the analysis is due to excessive wear of copper-containing engine parts, and/or whether the copper is a component of the motor oil being used. Even if the fleet operator knows that the crankcase was initially filled with oil of a known copper content, the operator still does not generally know from the analysis if wear is occurring, particularly if make-up oil was added. Thus, the make-up oil may be obtained from different suppliers, who may or may not have a copper additive in the oil. Furthermore, even if both the original oil and all make-up oil are from the same supplier, there may be an accumulation of metals, including copper, due to varying oil losses due to volatility of the base oil, which accumulation interferes with determining accurately the source of the copper.
The problem is to find a reliable method of determining whether any copper in the oil is due to a copper additive used by the oil manufacturer, or is due to other sources such as wear of copper-containing parts, or whether the copper is from both an oil additive and wear. It also becomes important to determine the relative amount of copper individually due to an oil additive and to wear to indicate whether the wear is excessive.